Trane ACONT900AC43UA Service Manual page 185

Measuring Flame Current
LED flash code
The furnace control will indicate a two flash code
when the furnace has locked out on flame detection.
Typically, this fault code is caused by a dirty flame rod
or a lack of proper inlet gas pressure (cold days when
the fuel line pressure falls below the minimum level
required to make the gas valve perform properly.) Natu-
ral gas furnaces require a minimum of 5" of water col-
umn at the inlet to the valve with the furnace opening
(both stages are applicable.); LP gas furnaces require
of minimum of 11" of water column. When checking
inlet pressure, make sure to turn all major gas appli-
ances on to simulate the highest demand on the gas
piping system.
Furnace control locks out
If the flame current is below one microampere, check
for a dirty flame rod or a cracked ceramic base on the
flame rod assembly. If these check out OK, and the
flame is surrounding the flame rod, check for a broken
flame current wire. If these all check out OK, replace
the flame rod assembly.
If the flame current is above one microampere, yet the
IFC continues to lock out on a flame current fault,
check for proper electrical ground and polarity of the
high voltage. If they are acceptable, replace the IFC.
GF - F 5